SEOUL, Feb 20 (Reuters) - South Korean octogenarian Jang Choon has bought a new suit, hoping to finally make it to North Korea this week to meet the family he has not seen since the 1950-53 Korean War.

Kim Dong-bin, a 78-year-old diagnosed with lung cancer in September, has been undergoing chemotherapy that he says will allow him to meet the elder sister he was separated from over 60 years ago before he dies.

Jang and Kim are among 82 South Koreans selected to make the trip north across the world's most heavily fortified border, a frontier that separates two countries that remain at war after their conflict ended in an armistice rather than a peace treaty.

The six days of family reunions scheduled to start on Thursday take place under the cloud of a U.N. report on human rights abuses in North Korea, which investigators have said were comparable to Nazi-era atrocities.

Pyongyang has rejected the report, describing it as a concoction by the United States and its allies, Japan and the European Union. But, the North appears to be willing to maintain a rapprochement with South Korea that may be crucial as it seeks food for its people.

"I am afraid my family in North Korea might still think I came to the South to live a good life for me alone," said Kim, who fled south when he was 16, fearing U.S. attacks on Pyongyang during the war.

"Before I die, I must explain that I did not abandon my family, that I was swept up by the refugee flow during the chaos. Resolving this misunderstanding is the first thing I want to do in person with my sister," he said, adding that chemotherapy was working for him.

The reunions used to be held roughly annually, but have not taken place for three years as tensions between the two Koreas spiralled higher after the South said the North sank one of its naval vessels in 2010. In later months, the North shelled a South Korean island and Pyongyang threatened nuclear attacks last year.

"My youngest brother Ha-choon had not even started school when I last saw him," said Jang, the eldest of four siblings, one of whom has died.

"But now he's an old man like me," said the 81-year-old, sporting the light brown suit and maroon tie that he has bought for what he believes will be his last meeting with his remaining brother and sister, who remain in the North.

Conscripted by the North Korean army at the age of 19, Jang was captured and, when given a choice to return to his home in North Hamgyong Province near the Russian border, he opted to stay in the South.

Of the 128,000 people registered in South Korea as coming from families that were torn apart by the Korean War, 44 percent have already died and more than 80 percent of survivors are over 70-years-old, according to South Korea's Unification Ministry, which handles inter-Korean relations.

CAN'T DIE WITH MY EYES CLOSED

Last September, the North abruptly announced an indefinite postponement of reunions that had been scheduled for shortly after the Korean Thanksgiving holidays.

This year it demanded that South Korea and the United States halt military drills at the price of holding the reunions, although it later said it would allow them, opening a door to potential dialogue between Seoul and Pyongyang.

The possibility of food shortages could have been a factor.

"Now it's almost March, when the new farming season must begin, and Kim Jong Un has no means to feed his people," said Kim Seok-hyang, professor of North Korean studies at Ewha Womans University.

"He must get outside help. But looking around, the U.S. won't give him anything, China doesn't seem willing to give anything and then there's the U.N. human rights report pressuring him. The family reunions card is his last resort because he can't neglect his people."

But South Koreans visiting the Mount Kumgang resort in the North have other issues in mind.

Kim, the cancer patient, has prepared gifts such as down jackets, socks and long johns for his sister.

"Winters are harsher up in the North and we know that heating systems are crude there," he said.

There have been 18 family reunions since the first in 1985 and a total of 18,143 South and North Korean brothers, sisters, fathers and mothers have met.

The events have never been regular and the two Koreas have squabbled over the details of the events, like deciding on the venue. After the first four, in which families traveled back and forth between Seoul and Pyongyang, North Korea has insisted on hosting the events on its soil.

"The North fears exposing their people to the outside world so they want to shroud their people from looking at the South's successful way of life," said Kim, the professor.

For the families, the politics are secondary.

"I swore to myself, I must not die before I meet my brother and sister," said Jang, the 81-year-old. "I just cannot die with my eyes closed if I don't see them this time." (Editing by David Chance and Raju Gopalakrishnan)